THE PH-DEPENDENCE OF FREE IONIC ACTIVITIES AND TOTAL DISSOLVED CONCENTRATIONS OF COPPER AND CADMIUM IN SOIL SOLUTION

Concentrations of total dissolved Cu and Cd and activities of their fr ee ions in soil solution are suggested to be influenced by soil pH. Th e objective of this research was to study the relationships between fr ee ionic activities and total dissolved concentrations of Cu and Cd an d soil pH. Soil samples from Elkhorn, WI, USA (Typic Argiudoll), were used as a model. Free ions Cu2+ and Cd2+ were determined in the soil s aturation extracts by using Donnan analysis with graphite furnace AAS. The values of soil pH beyond their indigenous values were obtained by additions of dilute nitric acid to the soil-water mixtures. The resul ts showed that logarithmic concentrations of total dissolved Cu and Cd showed curve-linear relationships with soil pH. Free ionic Cu2+ and C d2+ activities were negatively correlated with soil pH. The slopes of log (Cu2+) vs. pH plots were -0.10 and -0.30 and those of log (Cd2+) v s. pH plots were -0.60 and -0.70 for the control soil and the sewage-s ludge-treated soil, respectively. (C) 1998 Elsevier Science B.V.